1. Field of the Invention
The present invention relates generally to a duct type air conditioning system for a multi-zone space, and more particularly, to a variable air quantity control system capable of regulating temperature in each zone independently of each other in accordance with a time and temperature schedule.
2. Description of the Prior Art
Conventional residential air conditioning systems (which can provide both heating and cooling) are typically controlled with a single thermostat. Accordingly, the one set point in the thermostat will cause the temperature in the vicinity of the thermostat to be controlled to the desired level, but in other parts of the residence the temperature can vary widely due to heat load through windows, shading of spaces, heat generated by people or equipment, and various other factors. Thus, certain places in homes require more or less temperature control than others. Upstairs areas have drastically different heating/cooling requirements than downstairs areas or basements. Bedroom areas need temperature control only at certain times of the day or night. Homes with large areas of glass present several problems for maintaining a comfortable temperature. Most residences have areas that are exposed to direct sunlight during certain hours. In both Summer and Winter, those zones require different levels of heating or cooling than other part zones of the home. With a single centrally-located thermostat it is impossible to have optimum temperatures in all zones/rooms at all times. In a zoned residence, however, individual zones with differing heating/cooling properties and hours of use can be kept at optimum temperatures. One zoning method uses separate heating and cooling units to maintain different comfort levels in different parts of the residence. However, each system uses its own thermostat which is centrally located in a zone to be maintained by the respective system, but, because the separate units do not function as a system, they may over lap in heating and cooling some areas and perform as two independent systems.
To overcome the added installation costs, added expense to operate, and the overlap problems with dual equipment zoned systems, the use of one heating and cooling unit with a series of thermostats in each room can be provided. A single unit zoned system allows different parts of a residence to be controlled at different temperatures at different times by programming each thermostat in each zone for a desired temperature over a period of time. Although the one zoned heating and cooling unit offers cost savings, greater comfort, and greater flexibility by allowing the homeowner to set different temperatures throughout the house only during times of need or occupancy, these single heating and cooling units with multiple programmable thermostats also have some disadvantages. Conventional one heating and cooling zoned systems allow each individual thermostat to turn on the heating and cooling unit and operate the zone damper in the respective zones. In practice, this system is quite complicated to operate and inefficient because the several individual thermostats can turn the heating and cooling unit ON and OFF and each zone must be individually programmed for the desired temperature and schedule, and there is no central control. Often it is desirable to temporarily change a current setpoint in a single zone during the pre-set program period. Further, it is often desirable to temporarily prevent the current set point in a zone from changing with a pre-set program schedule. Still further, it is often desirable to temporarily change all zone setpoints and time schedules, e.g. during vacation periods. These problems require the user to re-program the controller for a short period and then re-program the controller again shortly thereafter to set in the original schedule.